Microporous styrene polymers and method of making same

ABSTRACT

Microporous styrene polymers are provided having randomly interconnected open network of irregularly shaped pores whose walls consist of cohered spherical particles of the polymer. These microporous styrene polymers are produced by mixing styrene polymer latex with a water-soluble ether, casting, molding, or impregnating the resulting mixture into a fibrous material, heating same to a temperature of from about 80*C to about 120*C and removing the ether.

O United States Patent l 91 [111 3,887,730

Rainer et al. June 3, 1975 1 MICROPOROUS STYRENE POLYMERS 3.489.827 1/1970 Mueller et al. 260/25 L x AND METHOD OF MAKING SAME 3,674,722 7/1972 Rain er et al 260/25 M 3.753.932 8/[973 Jenkins 260/25 L X [75] Inventors: Norman B. Rainer; Peter Allen Wilson, both of Richmond, Va. Assigneez Philip Morris lncorporaed New Primary Examiner-Thomas J Herbert, Jr.

York, NY.

[2]] Appl. No.: 282,481

Microporous styrene polymers are provided having randomly interconnected open network of irregularly [52] Cl 427/244; 428/904; 131/10 R; shaped pores whose walls consist of cohered spherical 260/25 Li 260/25 M; 427/245; 264/4 particles of the polymer. These microporous styrene [5l] int. Cl. 844d 1/09; A24d 1/00 polymers are produced by mixing Styrene polymer [58] held M Search 260/25 L; 131/10 latex with a water-soluble ether, casting, molding. or

131/10 R; 117/1 UB1 UZ impregnating the resulting mixture into a fibrous material, heating same to a temperature of from about [56] References cued 80C to about 120C and removing the ether.

UNITED STATES PATENTS 3,396,049 8/l968 Anderson ct al l l7/l6l UD X 12 Claims, N0 Drawings MICROPOROUS STYRENE POLYMERS AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION 1. Field of Invention This invention relates to a process for the preparation of microporous styrene homopolymers and copolymers and to the products obtained thereby. In one aspect, the present invention is directed to microporous polymers of styrene having improved microporosity and structure. In another aspect, the present invention is directed to microporous styrene polymers and to arti cles comprising such polymers. In one of its more specific aspects, the present invention concerns tobacco smoke filters comprising microporous polymers of styrene made according to the process of this invention.

2. The Prior Art The preparation of articles having microporous structures has received considerable attention in the prior art. Indeed there are several patents which disclose such articles, for various applications, and describe the methods of their preparation. For example, US. Pat. Nos. 2,777,824 and 3,055,297 describe the preparation of a synthetic thermoplastic polymer, such as, polyvinyl chloride, having a microreticulated structure by a method which basically comprises sintering a mixture of the resin, a plasticizer (e.g., dioctyl phthalate) and an organic liquid non-solvent for the resin (e.g., xylene) to a temperature at which the resin fuses while the system is under sufficient pressure to maintain the mixture in the liquid phase. Sintering at these conditions is continued until a microreticulated structure is formed and the non-solvent may be removed by heating and/or reducing the pressure. When used for tobacco smoke filtration, these products have not been entirely satisfactory since they frequently do not have the desired degree of uniformity and are not particularly effective in removing the undesirable constituents of the tobacco smoke stream.

U.S. Pat. No. 3,528,433 (Johnson et al.) also describes microporous structures for use in granular form as filter material for cigarettes. According to this patent, a thermoplastic synthetic resin such as polyvinyl chloride is heated together with an organic liquid which is non-solvent for the resin until the resin fuses and again heating is continued under a pressure sufficient to maintain the non-solvent in the liquid phase. The mixture may optionally contain a plasticizer for the resin which, together with the non-solvent liquid, are removed or extracted, after fusion of the resin, by contacting the fused resin with vapors of a second liquid. However, unless proper precautions are exercised, the pore structure of the resulting product will be nonuniform and hence it will not be highly effective in tobacco smoke filtration. Furthermore, when plasticizers are employed, the non-uniformity of the product will be aggrevated by the formation of an impermeable outer skin or sheath thereon.

It is noted from the foregoing description that the synthetic resin is employed as a dispersion of the resin in a non-aqueous liquid which is non-solvent for the resin. However, in a very recent patent, i.e., US. Pat. No. 3,674,722, issued July 4, 1972 the patentees who are also applicants of the present application disclose a method for the preparation of microporous polyvinyl chloride which has improved microporous structure. The process disclosed therein involves the use ofa vinyl chloride polymer latex, i.e., an aqueous suspension of vinyl chloride polymer in an organic liquid which is a non-solvent for the polymer. There are several differences in the manner of preparing the microporous structures of this invention from those described in this patent. These differences will become apparent from the ensuing detailed description of this invention.

SUMMARY OF THE INVENTION In accordance with this invention, polystyrene latex or a latex of a copolymer of styrene with other monomers such as, e.g., butadiene, acrylic acid, 2- (aminoethyl) methacrylate, styrene sulfonic acid, acrylonitrile, N-vinylpyridine and N-vinylpyrrolidone, is mixed with a water-soluble ether, the resulting mixture is cast, molded or impregnated into a fibrous material or other porous structure such as an open-celled foam which is then heated to a temperature of from about C to about 120C for about 1 minute to about 1 hour to form an open-celled porous structure wherein the pores are filled with the ether. If desired, the ether diluent may be removed from the structure by conventional extraction techniques using conventional extractants, in which case the resulting structure will contain air-filled pores.

DETAILED DESCRIPTION OF THE INVENTION It has now been discovered that microporous polystyrene and microporous copolymers of styrene with butadiene, or other comonomers, can be prepared using a polymeric latex as the starting material, and subjecting the polymeric latex to a series of controlled and critical operations designed to achieve a product having improved microporosity. Thus, polystyrene latex containing from about 10 to about 70 weight percent, and preferably from about-30 to about 60 weight percent of polystyrene solids is diluted with a water-soluble ether until the diluted mixture contains from about 5 to about 30 weight percent dispersed polystyrene solids. The polymeric latex which is employed is preferably of the non-film forming type because film-forming type latices will tend to coalesce to form a non-porous structure.

The ethers which are suitable as diluents in the process of this invention must be water-soluble and must have a boiling point above about C. Typical suitable ethers include: diethylene glycolmonoethyl ether, otherwise known in the trade as Carbitol, ethylene glycol monoethyl ether, otherwise known by the trade name Cellosolve, diethylene glycol monomethyl ether and ethylene glycol monomethyl ether, known by the trade names of "Methyl Carbitol and Methyl Cellosolve, respectively, or mixtures thereof. The ethers which are particularly useful in the practice of this invention are aliphatic and non-cyclic, although, certain aromatic and alicyclic ethers may also be suitably employed. If desired, a mixture of glycol ether may be employed together with a glycol such as propylene glycol, diethylene glycol, and triethylene glycol provided that the glycol content does not exceed about 50 weight percent of the mixture.

It is important in the present invention that the ether employed be watersoluble, non-solvent for polystyrene (or the styrene copolymer) and be compatible with, i.e.. not cause agglomeration of the latex. The ethers which are preferred in this invention conform to the following equation:

where 1.06 represents the density of the polystyrene.

The following table illustrates the applicability of the foregoing equation to several ethers which are useful as diluents for polystyrene latex in the practice of this invention.

After diluting the polystyrene latex as aforesaid, the dispersion mixture is placed in a mold or cast in the form of a fiat sheet, or is impregnated into a paper and the resulting mold, cast sheet or impregnated paper is then heated to a temperature of from about 80C to about 120C for about 1 to about 50 minutes to obtain the desired product. During the heating cycle, especially while the dispersion mixture is still in the liquid state, it is preferred to maintain quiescent conditions throughout the dispersion mixture. For molding of massive objects without confinement under pressure, one may, if desired, remove the water at lower temperature (at reduced pressure) prior to the heating step.

The following examples will further illustrate this invention.

EXAMPLE 1 Ninety grams of diethylene glycol monoethyl ether was added slowly to grams of a polystyrene latex containing 50 percent solids while the mixture was stirred continuously. The resultant mixture was a homogenous milky-white dispersion. This mixture was applied to a tissue paper having a porosity of 6 seconds as measured by the Greive method, by immersing the paper in the dispersion and then permitting excess dispersion to drip off while hanging vertically. The impregnated paper was then suspended from a glass rod across the top of the beaker and was heated at 100C for 30 minutes. The treated paper was then washed with water and then dried. The resultant paper was considerably more opaque and white than the untreated paper and it was porous and exhibited high absorbtivity for oil.

Photomicrographs of a treated paper sample made according to this example taken at 160X magnification at different points of the treated paper. revealed the presence of microporous deposits filling the spaces between cellulosic fibers of the paper.

It is also possible to use a polystyrene latex wherein the individual polymer particles have been colored by absorption of an organic dye. Papers treated by the process of this invention using such colored latices become durably pigmented with the polymer.

EXAMPLE 2 Ninety grams of diethylene glycol monoethyl ether was added to 25 grams of a polystyrene latex to form a dispersion containing 10 percent polystyrene solids. A sample of this dispersion was placed in a sealed Carius tube and was heated in an oven at 100C for about 60 minutes while maintaining the tube therein in a horizontal position. After this heating period the material in the tube had sintered into a rod.

The tube was thereafter removed from the oven and cooled to room temperature. The sintered rod was removed from the tube, diced into chips and washed with water. These chips were then ground in a Waring blender employing sufficient water to form a thin slurry. The slurry was sieved with the aid of a flowing stream of water to obtain 40/80 mesh granules. A photomicrographic examination of a washed and dried chip revealed a porous structure, and the granules. when examined microscopically at 100X amplification, were found to have some degree of ciliation. These granules were also determined to have pore volume greater than 3.4 cc/g and their average pore diameter was 0.6 microns, as determined via a Mercury lntrusion Porosimeter.

When tested for tobacco smoke filtration, these granules showed 65 percent removal of total particulate matter (TPM) with a mg. loading at 5 inch resistance-to-draw (RTD). This test was carried out in accordance with the standard test method described in the Journal of the Association of Official Agricultural Chemists, Vol. 47, no. 2, April 1964, pp. 356.

EXAMPLE 3 Seven and one-half grams of polystyrene latex was diluted with 17 grams of diethylene glycol monoethyl ether to obtain a dispersion containing 15 weight percent of the solid polymer. A sample of this dispersion was placed in an open petri dish to a depth of about 3 mm. layer and heated in an oven at C for a 40- minute period, after which the dish was removed from the oven and cooled to room temperature. After this period, the material had sintered into a microporous sheet. This sheet was washed with water to remove the ether and then dried. The resulting sheet was strong and flexible and had an average effective pore size of 5 microns as determined by the filtration of dispersions having known particle sizes.

EXAMPLE 4 The method of Example 3 was followed except that the diluent was an equal mixture of diethylene glycol monoethyl ether and propylene glycol and the resulting dispersion contained 20 weight percent solid polymer. The resulting sheet was microporous and was found to be useful as a filterf EXAMPLE 5 The method of Example 3 was followed again except the diluent was en equal mixture of diethylene glycol monoethyl ether and propylene glycol and the latex was a copolymer of styrene with butadiene containing 80 weight percent of styrene. The mixture was diluted to a dispersion containing weight percent solid copolymer. The resulting sheet in this example was microporous, had excellent strength, and its effective filtration pore size was between 0.1 and 0.5 micron.

As shown in Examples 1-5, both homopolymers of styrene as well as copolymers of styrene latices can be employed in the process of this invention. When using copolymers of styrene, the comonomer may be butadiene, acrylic acid, Z-(aminoethyl) methacrylate, styrene sulfonic acid, acrylonitrile, N-vinylpyridine and N- vinylpyrrolidone. Moreover, the styrene monomer content of the copolymer must range from about 70 to about 98, preferably from about 80 to about 90 weight percent of the copolymer.

As is evident from the foregoing examples, the microporous products of this invention find particular usefulness as a tobacco filter material for effective tobacco smoke filtration. It has also been found, however, that a paper impregnated with microporous polystyrene produced in accordance with this invention is heat sealable to form bags, envelopes, containers and packages without the application of glue or other adhesive materials. Furthermore, the microporous polystyrene of this invention may be chemically treated by known methods to produce polystyrene having ion-exchange characteristics.

What is claimed is:

l. A process for preparing a microporous product which process comprises:

a. diluting a styrene polymer latex, said styrene polymer being non-film forming and comprising at least 80 percent styrene, with a water-soluble ether compatible with said polymer and having a boiling point above about 85C, said ether being employed in an amount sufficient to form a dispersion con taining from about 5 to about. 30 weight percent of said polymer,

b. impregnating said dispersion into a fibrous material, and

c. heating the impregnated fibrous material to a temperature of from about 80C to about 120C, said temperature being lower than the boiling point of said ether, for about 1 minute to about 60 minutes.

2. The process of claim 1 wherein said ether is removed from said heated impregnated fibrous material.

3. The process of claim 1 wherein said polymer is polystyrene.

4. The process of claim 2 wherein said polymer is polystyrene.

5. The process of claim 1 wherein said polymer is a copolymer of styrene and a monomer copolymerizable with styrene.

6. The process of claim 2 wherein said polymer is a copolymer of styrene and a monomer copolymerizable with styrene.

7. A process for preparing a microporous product which process comprises:

a. diluting a styrene polymer latex, said styrene polymer being non-film forming and comprising at least 80 percent styrene, with a water-soluble ether compatible with said polymer and having a boiling point above about 85C, said ether being employed in an amount sufficient to form a dispersion containing from about 5 to about 30 weight percent of said polymer,

b. forming said dispersion into a shaped article, and

c. heating said dispersion in said shaped article at a temperature of from about 80C to about 120C, said temperature being lower than the boiling point of said ether, for about 1 minute to about 60 minutes.

8. The process of claim 7 wherein said polymer is polystyrene.

9. The process of claim 7 wherein said polymer is a copolymer of styrene and a monomer copolymerizable with styrene.

10. The process of claim 7 wherein said ether is removed from said heated dispersion.

11. The process of claim 10 wherein said polymer is polystyrene.

12. The process of claim 10 wherein said polymer is a copolymer of styrene and a monomer copolymerizable with styrene.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENTNO. 3,887,730 i DATED June 3, 1975 vE T0R(5) Norman B. Rainer and Peter Allen Wilson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, the formula before line 5 should read p e 35 M Col. 3, the formula before line 15 should read 1.06 P 5 a M Signed and Scaled this Twenty-third D f y 1978 C |S I.-\l.|

Am's't:

RU'IH (I MASON LUTRELLE F. PARKER Q Arresting Officer Acting Commissioner of Patents and Trademarks 

1. A PROCESS FOR PREPARING A MICROPOROUS PRODUCT WHICH PROCESS COMPRISES: A. DILUTING A STYRENE POLYMER LATEX, SAID STYRENE POLYMER BEING NON-FILM FORMING AND COMPRISING AT LEAST 80 PERCENT STYRENE, WITH A WATER-SOLUBLE ETHER COMPATIBLE WITH SAID POLYMER AND HAVING A BOILING POINT ABOVE ABOUT 85*C, SAID ETHER BEING EMPLOYED IN AN AMOUNT SUFFICIENT TO FORM A DISPERSION CONTAINING FROM ABOUT 5 TO ABOUT 30 WEIGHT PERCENT OF SAID POLYMER, B. IMPREGNATING SAID DISPERSION INTO A FIBROUS MATERIAL, AND C. HEATING THE IMPREGNATED FIBROUS MATERIAL TO A TEMPERATURE OF FROM ABOUT 80*C TO ABOUT 120*C, SAID TEMPERATURE BEING LOWER THAN THE BOILING POINT OF SAID ETHER, FOR ABOUT 1 MINUTE TO ABOUT 60 MINUTES.
 1. A process foR preparing a microporous product which process comprises: a. diluting a styrene polymer latex, said styrene polymer being non-film forming and comprising at least 80 percent styrene, with a water-soluble ether compatible with said polymer and having a boiling point above about 85*C, said ether being employed in an amount sufficient to form a dispersion containing from about 5 to about 30 weight percent of said polymer, b. impregnating said dispersion into a fibrous material, and c. heating the impregnated fibrous material to a temperature of from about 80*C to about 120*C, said temperature being lower than the boiling point of said ether, for about 1 minute to about 60 minutes.
 2. The process of claim 1 wherein said ether is removed from said heated impregnated fibrous material.
 3. The process of claim 1 wherein said polymer is polystyrene.
 4. The process of claim 2 wherein said polymer is polystyrene.
 5. The process of claim 1 wherein said polymer is a copolymer of styrene and a monomer copolymerizable with styrene.
 6. The process of claim 2 wherein said polymer is a copolymer of styrene and a monomer copolymerizable with styrene.
 7. A process for preparing a microporous product which process comprises: a. diluting a styrene polymer latex, said styrene polymer being non-film forming and comprising at least 80 percent styrene, with a water-soluble ether compatible with said polymer and having a boiling point above about 85*C, said ether being employed in an amount sufficient to form a dispersion containing from about 5 to about 30 weight percent of said polymer, b. forming said dispersion into a shaped article, and c. heating said dispersion in said shaped article at a temperature of from about 80*C to about 120*C, said temperature being lower than the boiling point of said ether, for about 1 minute to about 60 minutes.
 8. The process of claim 7 wherein said polymer is polystyrene.
 9. The process of claim 7 wherein said polymer is a copolymer of styrene and a monomer copolymerizable with styrene.
 10. The process of claim 7 wherein said ether is removed from said heated dispersion.
 11. The process of claim 10 wherein said polymer is polystyrene. 